How do you determine the circumference of a semicircle?

A:

The perimeter of a semicircle is 1/2 of the circumference of the corresponding complete circle plus the diameter of the circle. The distance around the outside of a semicircle is generally called its perimeter.

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A semicircle can be seen as the shape that is formed when a circle is cut in half along its diameter. The arc that remains as a part of the semicircle is half as long as the circumference of the whole circle. The perimeter of the semicircle also includes the straight line that connects the two ends of that arc. That line is the same length as the diameter of the original circle.

The perimeter of the semicircle is the length of its arc plus the length of the line that closes the shape and can be calculated using these equations:

A regular pentagon has rotational symmetry. The order of its rotational symmetry is five, because it can be rotated into five different configurations that look exactly the same before returning to its original configuration. The angle of rotation for each turn is 72 degrees.